Mechanical properties of Michigan Basin\u27s gypsum before and after saturation

The stability analysis of an abandoned underground gypsum mine requires the determination of the mine pillar\u27s strength. This is especially important for flooded abandoned mines where the gypsum pillars become saturated and are subjected to dissolution after flooding. Further, mine pillars are subjected to blast vibrations that generate some level of macro- and micro-fracturing. Testing samples of gypsum must, therefore, simulate these conditions as close as possible. In this research, the strength of gypsum is investigated in an as-received saturated condition using uniaxial compressive strength (UCS), Brazilian tensile strength (BTS) and point load index (PLI) tests. The scale effect was investigated and new correlations were derived to describe the effect of sample size on both UCS and BTS under dry and saturated conditions. Effects of blasting on these parameters were observed and the importance of choosing the proper samples was discussed. Finally, correlations were derived for both compressive and tensile strengths under dry and saturated conditions from the PLI test results, which are commonly used as a simple substitute for the indirect determination of UCS and BTS

An experimental investigation into the load transfer mechanisms in anchored geosynthetic systems.

An experimental investigation of the load transfer mechanisms in anchored geosynthetic systems has been performed. The objective of the research was to evaluate the ability of these systems to effectively apply a compressive load to cohesionless soil. Laboratory tests were conducted to investigate the load transfer mechanisms at the following three interfaces: (1) the anchor-soil interface, (2) the anchor-geosynthetic interface, and (3) the geosynthetic-soil interface. Cyclic pullout tests on ribbed anchors were conducted to study anchor-soil interaction. In dense sand a high interface friction developed during initial driving. However, upon load reversal it decreased by approximately 50%. Extreme degradation of the interface friction resulted with continued cycling. In loose sand, the maximum interface friction was approximately equivalent to the residual shear strength of the sand. The residual interface friction was about 50% lower than the maximum interface friction. Anchor-geosynthetic connection tests and wide-width tensile tests yield similar fabric strengths as long as the geosynthetic is firmly clamped in the connector. However, for a woven geosynthetic, where the weave can separate, a reduction factor had to be applied to the standard wide-width tensile test to predict the connection strength. Geosynthetic-soil deformation tests were conducted to determine the magnitude and distribution of the vertical stresses applied to the soil at the geosynthetic-soil interface. While significant soil stresses were observed in the vicinity of the anchor, they diminished rapidly with radial distance from the anchor. Finally, plastic yielding of the geosynthetic, combined with anchor uplift, may reduce stress in the system and thereby compromise the overall effectiveness of anchored geosynthetic systems in transferring load to the soil.Ph.D.Civil EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/105805/1/9208678.pdfDescription of 9208678.pdf : Restricted to UM users only

Slope Movement in Permafrost near Fairbanks, Alaska

A section of oil pipeline near Fairbanks, Alaska is experiencing hillslope movement. While the pipeline’s support system was designed to handle large movements, the slope movements are starting to exceed the anticipated design requirements. The pipeline was constructed on low angle permafrost slopes composed of Fairbanks silt. The silt occurs in three relatively distinct layers; an upper active layer, followed by an ice-rich silt layer overlying a non-ice rich silt layer. Based on inclinometer data, the slope movement is occurring near the ice-rich layer/non-ice layer interface at a rate of 4.5 cm/year. A traditional slope stability back analysis indicates that for slope instability to develop, the ice-rich layer (assumed the weakest) would require the layer’s friction angle to be in the range of about three degrees; much lower than traditional strength values would suggest. While some small underground gold mine shafts are located about 100 meter from the base of the slope movement, it is speculated that an additional factor causing slope creep is the syngenetic formation of the permafrost, which formed in successive frozen layers during freezing. Recent research has also suggest the possibility of cold weather neoformation of smectic clays developing that could assist in slope creep

Laboratory study of gypsum dissolution rates for an abandoned underground mine

Groundwater reestablishment in abandoned gypsum mines causes pillar dissolution until the groundwater reaches the groundwater’s gypsum saturation potential. In some cases, however, especially in shallow mines, groundwater can continue to flow through the mine resulting in the additional dissolution of the mine’s support pillars leading to possible pillar collapse. Pillar dissolution will depend on the amount and quality of the groundwater flowing through the mine and the dissolution rate of the gypsum. The Domtar Mine in Grand Rapids Michigan operated for over 140 years mining a 30-m-deep high-quality gypsum deposit. In 2000, the mine was abandoned with the removal of the mine’s dewatering pumps allowing the groundwater to flood the mine. The mine is located along the north side of the Grand River and has groundwater flowing through the mine to the Grand River. Interstate I-196 is located over the east side of the mine. To analyze the stability of the mine’s pillars, the gypsum dissolution rate was investigated. In this research, laboratory experiments were conducted to investigate the dissolution rate of natural gypsum in both stagnant and flowing water. The existing published dissolution rates were reviewed and compared to the investigation’s results. The tests confirmed that the dissolution can be represented by a first-order kinetic equation. The normalized dissolution coefficient was measured for stagnant water at 1.6 × 10−3 (cm/s) following the power law of k = 0.0021F0.1854 for flowing water, where F is the water’s flow rate and k is dissolution coefficient

Analysis of drying and saturating natural gypsum samples for mechanical testing

The stability of underground abandoned gypsum mines is dependent on the gypsum pillar's strength, and most abandoned mines are in a fully saturated condition. Moisture affects the strength of gypsum and is therefore commonly measured when testing rock strength. For most rocks, this is a simple task of weighing the rock's mass before and after oven-heating at a specified temperature and duration. For natural gypsum, however, this is not a straightforward process. Heating natural gypsum can result in dehydration and transformation of gypsum to hemihydrate and anhydrite, thus changing the physical characteristics of the gypsum such as its particle density which in turn affects the moisture content and strength measurements. To prevent transformation when determining the moisture content of gypsum, the American Society for Testing Materials (ASTM) recommends lowering the drying temperature from 110 °C to 60 °C. To investigate the temperature at which gypsum transforms to hemihydrate, we used a helium pycnometer to measure the particle densities of gypsum, hemihydrate and anhydrite. In this research, we suggest that a higher drying temperature of 80 °C can be used for drying gypsum without transforming gypsum to hemihydrate. Further, preparing saturated samples for mechanical testing, which is required in stability analyses of abandoned mines, is challenging due to the dissolution of gypsum when placed in water. To address this problem, we investigated the following methods to saturate gypsum cores taking into account the solubility of gypsum: (1) water immersion, (2) vacuum saturation, and (3) improved vacuum saturation. The research indicates that all the three methods are acceptable but they should be conducted using a saturated gypsum-water solution to minimize dissolution. Further, the research found that the improved vacuum saturation method saturated the test samples within 24 h, while duration of 30 h was required for the other two methods. Keywords: Gypsum-hemihydrate-anhydrite transformation, Dehydration, Rock core saturation, Moisture content, Helium pycnomete

Tropical storm-induced landslide-dammed lakes and debris flow hazards at Ocotepeque, Western Honduras

© 2018, Springer-Verlag GmbH Germany, part of Springer Nature. One of the deadliest tropical storms on record in Central America is the 1934 tropical storm that resulted in over 3000 fatalities; the majority of fatalities caused by floods, debris flows, and landslides. The hardest hit region was in western Honduras near the city of Ocotepeque, where 64 cm of rain fell on June 4, 1934. The rainfall caused a rock landslide forming a natural dam in a mountain valley above Ocotepeque. The dam failed 3 days later on June 7. The ensuing debris flow destroyed Ocotepeque killing an estimated 486 people, over 10% of the city’s population. There was little to no reporting of this disaster due to the city’s remote location and lack of adequate communications. Following this event, the city was relocated 4 km north of Ocotepeque and renamed Nueva Ocotepeque. Over time, however, the old location, Ocotepeque, was resettled and called Antigua Ocotepeque. In this study, we examine the 1934 event and the effects of a similar recurrence on both Antigua Ocotepeque and Nueva Ocotepeque. Landslide hazard maps of the area (for shallow landslides) were generated and used to investigate the possibility of landslide dams forming. The potential debris flow inundation areas were predicted, and the effects of potential debris flows were investigated. Deterministic slope stability analyses conducted on the new location indicated that potential landslides could be more significant than suggested by the current hazard maps

Tactile pressure sensors to measure ground pressure from tractor tire loads

This article provides an assessment of tactile sensors used to measure ground pressures in soil from full-size tractor tires. To capture the tire’s soil pressure four 5400N tactile pressure sensors from Tekscan (Boston, MA) were utilized with a full-size agricultural tire in a laboratory setting. A servo-hydraulic loading system, capable of both load and displacement control, was used to apply known tire loads to the soil with the sensor placed at a depth of 45 cm in a soil bin. Two full-size tractor tires were tested; a traditional tractor tire, W800/70R38, and a recently developed low-aspect-ratio tire, IF800/55R46. The sensors were conditioned and equilibrated before placement at the bottom of the soil bin in the laboratory, while a two-point calibration scheme was used to calibrate the sensors, resulting in a confidence level of 99 %. The sensors were successfully utilized in measuring the tire pressure in soil, which included the contact area, average ground pressure, and peak ground pressure on loose sand. As expected, the experiments show the contact area, and average and peak ground pressure increase with increasing the tire load and inflation pressure. Comparing the two tires tested at different loads and inflation pressures showed only minor differences in the recorded contact area, average ground pressure, and peak ground pressure

A dynamic damage growth model for uniaxial compressive response of rock aggregates

A model that combines damage evolution theory with dynamic crack growth is developed to investigate the uniaxial compressive response of rock aggregate. A damage parameter that determines the time at which the rock looses its ability to transmit the stress completely is introduced into the model. Flaw distribution in rocks is described by a two parameter Weibull distribution. The model correlates the damage parameter with the dynamic growth of wing cracks from the pre-existing microcracks. Influences of model parameters on stress-strain response and failure strength are studied systematically. The results of the dynamic damage evolution model are compared to the experimental observations on three types of rock and a good correlation is obtained. © 2002 Elsevier Science Ltd. All rights reserved

Investigating large landslides along a river valley using combined physical, statistical, and hydrologic modeling

Combined landslide susceptibility mapping and temporal early warning of failures can be a powerful method for mitigation and timely evacuation, but modeling must be well informed by the specific failure types and triggers unique to each climate and geomorphology. This paper describes the development of a landslide susceptibility map and threshold for riverbank erosion-triggered landslides in a northern climate with atypical landslide conditions. Located on the southern shore of Lake Superior, the Ontonagon River basin in northern Michigan receives an average of 4.8 m of snowfall annually, followed in the spring by a sharp warming trend and rain. Undercutting of the steep riverbanks causes large failures that continuously threaten bridges and a nearby hydroelectric facility. In this investigation, a landslide inventory was mapped using aerial imagery from 1992 to 2016. Landslide triggering factors were interpreted using temperature, cumulative precipitation, and river discharge data, demonstrating that river discharge is the primary predictor of landslides despite the source being either rainfall or snowmelt. A preliminary threshold was then created to determine the discharge characteristics likely to cause failures. A susceptibility map was created for the river system using a combination of Scoops3D with logistic regression, improving overall accuracy to 93%. Furthermore, Scoops3D proved valuable in constraining the model to failures of engineering significance (large volume and impact) and kinematic possibility. The threshold-susceptibility scheme is thus a powerful tool for assessing comprehensive slope stability along river channels